1. Field of the Invention
The present invention relates to a technique for identifying a face of a person included in an image.
2. Description of the Related Art
Along with the popularization of digital still cameras (to be also described as “DSC” hereinafter), many image data (several thousands to several ten thousands of image data) are sometimes required to be handled. As an especially important technique as a handling method, images are handled using faces of persons, thus implementing person extraction.
The person extraction method is roughly classified into a face detection technique and personal recognition technique. The former technique is used to find out a face included in an image, and is used in judgment as to whether or not a face is included. The latter technique is used to specify a person of the detected face. Upon execution of person extraction, in order to identify each person, a database (face dictionary) used to store face feature patterns for respective persons is referred to. Then, based on images registered in the face dictionary, analysis processing of a newly added image is executed to implement person extraction.
Japanese Patent Laid-Open No. 2005-208850 (to be referred to as literature 1 hereinafter) discloses a technique which uses feature amounts of a plurality of different expressions and probability distribution parameters upon execution of personal recognition.
On the other hand, Japanese Patent Laid-Open No. 2011-134114 (to be referred to as literature 2 hereinafter) describes a precision drop prevention technique in association with variations of illuminations, directions of faces, and changes of expressions at the time of recognition. In association with each of a plurality of dictionary data prepared for respective data attributes, a correlation value between corresponding local patterns of input data and dictionary data is calculated. Sets of correlation values for respective data attributes are integrated to calculate a similarity of the input data, and identification is made based on that similarity.
Note that as a technique for updating a dictionary based on a recognition result using a recognition dictionary, Japanese Patent Laid-Open No. 06-095685 (to be referred to as literature 3 hereinafter) is available.
Patent literatures 1 and 2 above include descriptions corresponding to changes of expressions and illuminations so as to improve personal recognition precision, but the personal recognition precision is not sufficient.